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Cloth modeling

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What is the best way to model cloth when it is to be used in a real-time application, like a game? Thinking about Constraints, Collision, Physical vs Geometrical, Partical etc. To be used in a master thesis! Any other information about cloth simulation/modeling will be appreciated.

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I am afraid I''m not going to be giving you any serious help because I''ve never tried to model cloth but it seems to me there is an obvious issue here which you need to address: people are very unlikely to own a computer which can handle accurately modelled cloth within a game enviroment unless the game is called "watch the accurately modelled cloth". So straight away I think you need to be asking yourself "what''s the best way to fake it?"
For most game purposes keyframe animation would be the quickest and easiest method. As long as you have a few different animations for different situations this would look fine, but for a master thesis you will indeed want to walk the road of physical simulation in which case I offer the following advice:

Forget collision detection for anything other than the floor- it will use as much processing power as the rest of your application put together if you put your cloth in anything other than the simplest of environments (i.e. an empty cube).

You will need to simulate two forces acting on your cloth: gravity and atmospheric forces(air). Gravity is easy - things are pulled down with a force of approximately 10 Newtons, which will give them an acceleration of 10 m/s/s unless something gets in their way, such as air. Air resistance is a bastard to simulate so my advice would have to be "don''t do it" but then not everyone is as lazy as me. Working out and applying the aerodynamics of a car would be a mammoth task but to do the same with a cloth, which has different aerodynamic properties every time it moves (i.e. nearly every frame) does not bear contemplation (for me). So you''ll want to fake it - apply air resistance according to a preset "aerodynamics" value for the cloth which doesn''t change. Less accurate but you might actually finish your project. It''s probably easiest to treat wind as seperate from air resistance, though in reality they are part of the same thing - the atmosphere. First move your cloth appropriately in the direction of the wind according to its weight, its constraints(if its tied to anything) and the windspeed then deform your cloth with a sine wave travelling in the direction of the wind, increasing the speed and amplitude of the wave as the windspeed increases. To work out how the cloth should perform when given constraints or hitting the floor I would probably give it a skeleton, bizarre though this sounds. Faking it like this you could reasonably expect to put your cloth in a game and still have some other stuff going on but in reality no one would let you because it would still drain too many resources. Maybe in a few years...

Hope this gave you something to think about. Be aware that I am merely a bedroom programmer and just trying to apply common sense to the problem rather than experience. Good luck - simulating cloth is one of the hardest things I can think of.
-


Geocyte Has Committed Suicide.

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Intel has an article online about the subject
http://cedar.intel.com/cgi-bin/ids.dll/content/content.jsp?cntKey=Generic+Editorial%3a%3aclothsample&cntType=IDS_EDITORIAL

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Guest Anonymous Poster

Try:

String

Cloth

Gel for kicks

Check out the rest of his page too. Very cool page.

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Guest Anonymous Poster

Try:

String

Cloth

Gel for kicks

Check out the rest of his page too. Very cool page.

If there is a double post, it is due to catching an error.

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Thanks

A lot of good advice here, especially from Geocyte. Have already looked at the articles suggested as well as the site, but still, thank you.
I will need to think a bit and do some more reading, but I will get back later with some new questions

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Jerry Weil, "The Synthesis of Cloth Objects", SIGGRAPH 1986, pages 49-54. (If you''re an ACM/ACM SIGGRAPH member it''s available for download.)

Watt & Watt, "Advanced Animation & Rendering Techniques", Addison Wesley, pages 417-419. (Covers the method in the above paper.)

I''ve seen a more recent method (can''t remember where unfortunately) which worked with something similar to a spring function where the weights of a few key threads after the application of a physics model were interpolated to give the in-between threads.

--
Simon O''''Connor
Creative Asylum Ltd
www.creative-asylum.com

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Hey S1CA, I was just wondering how do you become a member of SIGGRAPH? I''ve seen some of the stufff they''ve done mentioned before and its very impressive.

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www.siggraph.org

Click on the membership link and then the Join ACM SIGGRAPH link.

ACM SIGGRAPH is simply an organisation for people interested in computer graphics and research into it. It holds an annual conference where new papers are published and talks/tutorials are given. Keeping up to date with the papers/conference keeps you up to date with the thoughts and research of some of the cleverest graphics people in the world.


SIGGRAPH admin appears to be in New York though so due to unfortunate terrorist incident there yesterday the manual part of the admin (i.e. magazine & printed conference proceeding mailout etc) may be adversely affected.


--
Simon O''''Connor
Creative Asylum Ltd
www.creative-asylum.com

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Guest Anonymous Poster
I am going to give some links that go from simple and robust to more advanced. I used these when I wrote a small demo of a cloth sim, and of all the resources I checked out, these were the best/most fun:

Physical modelling in general:
http://www.cs.cmu.edu/~baraff/sigcourse/index.html

Particle simulation:
http://www.darwin3d.com/gdm1999.htm

Stable and easy to understand implementation:
http://www.ioi.dk/Homepages/tj/publications/gdc2001.htm

More advanced integration schemes:
http://www-2.cs.cmu.edu/~baraff/papers/sig98.pdf

More real time advanced integration:
http://www-grail.usc.edu/pubs/DSB_GI99.pdf

Also check these out:
http://www-grail.usc.edu/
http://www.cs.caltech.edu/~mmeyer/Research/Cloth/
http://www-grail.usc.edu/pubs/DMB_chapterBook.pdf
http://miralabwww.unige.ch/ARTICLES/JWS97-B.html

/Joakim

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Thanks

Some good links here. Have seen some of them, ut hey, they are still good

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